<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style>
        /* 鼠标聚焦的时候变颜色 */
        input:focus{
            color: aqua;
        }
    </style>
</head>
<body>
    <input type="text">
</body>
</html>